This invention relates to an apparatus for absorptiometric analysis in the field of automatic chemical analysis apparatus and, more particularly, to an absorbance measuring apparatus which can quickly effect absorbance measurement processes on a number of samples for a plurality of measurement items.
FIG. 1 shows a conventional absorbance measuring apparatus. A beam emitted from a light source 10 is incident on a bundle of optical fibers 12 and is led through these optical fibers 12 to reaction tubes 20 for a plurality of channels located in, for instance, three measuring stations, i.e., first to third measuring stations 14, 16 and 18. In the illustrated example, each measuring station has four channels, though a reaction tube for only one of these channels is shown for each measuring station. Reflecting mirrors 22 are each disposed on the side of each reaction tube 20 opposite the beam emission end of the corresponding optical fiber. The beam emitted from each optical fiber 12 is transmitted through a reaction liquid contained in each reaction cuvette 20 and is then reflected by each reflecting mirror 22. Beams reflected from the individual reflecting mirrors 22 are incident on two-wavelength spectrometers 24, 26 and 28, respectively. Each of the two-wavelength spectrometers includes a beam splitter 30 and spectrometers 32 and 34. The beam splitter 30 splits the incident beam into two light beams which are led to the pair of spectrometers 32, 34. The spectrometers 32, 34 each include a filter and a photo-detector, and can measure the intensity of transmitted light of particular wavelengths.
A sample serum, for example, is distributed to the reaction tubes 20 for four channels, and different reagents for the respective channels are poured into the sample serum in the individual reaction tubes 20. The reaction tubes 20, each of which contains the reaction liquid, i.e., the mixture of sample serum and reagent, are brought to the successive first to third measuring stations 14, 16 and 18, and the intensity of the transmitted beam is measured for two different wavelengths at each of the measuring stations. Changes in the absorbance (i.e., the reaction degree) of the reaction liquid, over time, can thus be measured, whereby an examination can be conducted for four different channels of items (such as GOT and GPT) in the respective samples.
In this absorbance measuring apparatus, two-wavelength spectrometers 24, 26, 28 must be provided for the individual channels at the respective measuring stations. Therefore, the cost and size of the apparatus are increased to that extent. Further, since changes in the absorbance of each reaction liquid, over time, are measured by different two-wavelength spectrometers 24, 26, 28, the results of examination are subject to error, due to variations in the light-electricity conversion characteristics among the individual two-wavelength spectrometers 24, 26, 28. This is a serious drawback; and, where examination is done by measuring the enzyme activities of GOT or GPT, which can undergo fewer absorbance changes, the drawback is so serious that the examination becomes impossible. Moreover, the optical fibers 12 have a low filling factor, so that a high output halogen lamp which continuously emits light is used as the light source 10. A beam of such a high energy level, however, would cause decomposition of a reaction liquid obtained from, for instance, the serum of a jaundice patient, thus disabling accurate examination.
FIG. 2 shows a different conventional absorbance measuring apparatus. In this case, a plurality of reaction cuvettes 46 are disposed along a circle for each of the different channels 36, 38, . . . . The reaction cuvettes 46 for each channel are moved about the center of the circle. When each reaction cuvette 46 is at an absorbance measuring position, a beam emitted from a light source 48 is converged by a condenser lens 50 and transmitted through the reaction liquid in the reaction cuvette 46. The transmitted beam is passed through a slit 52 to be incident on a diffracting grating 54. Diffracted monochromatic light beams from the diffracting grating 54 are detected in a photodiode array 56. In each of the channels 36, 38, . . . a particular item of examination is done, that is, the same reagent is poured into the reaction cuvettes 46 in the same channel. A sample, e.g., a serum, is distributed through a tube 42 and pipette 44 into the reaction cuvettes 46 in the same channels 36, 38, . . . . In each tube, it is mixed with a reagent so that a reaction liquid is produced. Changes in the absorbance of the reaction liquid with time are measured by each diffracting grating 54 and photodiode array 56.
In this apparatus, the absorbance is measured by the same spectrometer (i.e., by diffracting grating 54 and photodiode array 56) for each particular item, and the measurement is thus free from errors due to fluctuations of the spectrometer's detection characteristics. However, the light source 48 must be provided for each channel. Therefore, the operation and service are rather cumbersome. In addition, high power must be consumed for driving the light sources. Further, the size of the apparatus is inevitably large.
According to the invention disclosed in U.S. Pat. No. 3,697,185, while a sample such as a serum flows through a tube, a reagent is added to the sample, and the absorbance of the resultant reaction liquid is measured under temperature-controlled conditions. The measurement of absorbance is done by causing filtered beams of particular wavelengths to be incident on the reaction liquid at successively provided measuring stations.
In this apparatus, measuring stations are provided for the respective wavelengths of the absorbance measurement, so that an enlarged apparatus is again inevitable. In addition, it is probable that stray light which is incident on the detector will cause an error in the detection. Further, the precision of detection is influenced by the balance of the filter.